This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Neutralizing antibodies in HIV-1 infection are directed against the envelope (Env) glycoproteins gp120 and gp41. However, HIV-1 Env utilizes highly effective, but poorly defined, mechanisms to evade antibody-mediated neutralization. Our lack of information about the B cell responses, targets of autologous neutralization, and mechanisms of viral escape in subtype C infection represents a significant gap in our understanding of the most predominant HIV-1 variants worldwide. The objective of these studies continues to be identifying B cell targets and defining mechanisms of virus neutralization and escape in newly infected subtype C patients using a unique set of reagents derived from newly subtype C HIV-1 infected subjects in a Zambian cohort. This project was renewed for an additional five years of funding during the reporting period. During this period, we have characterized the initial autologous Nab response against the infecting virus, and the viral escape pathways that ensue, in unprecedented detail in two subtype C HIV-1 infected Zambian subjects. Neutralizing antibodies initially target the surface exposed hyper-variable domains of the envelope, and the virus uses multiple molecular pathways and compensatory mechanisms to escape from neutralization, even within a single patient. We have generated two monoclonal antibody producing B cell hybridomas from one of these Zambian subjects, and mapped the autologous neutralization targets and viral escape mutations. We have collected additional viable PBMC from this subject to isolate monoclonal antibodies with different specificities. We have collected longitudinal plasma and viably frozen PBMC samples from 10 additional subjects in Zambia for expanded studies of neutralization and escape, and generation of more B cell hybridomas that produce autologous neutralizing monoclonal antibodies.